The present invention relates generally to lasers employing phase conjugate reflecting elements, and in particular, to phase conjugate lasers wherein the phase conjugate reflector is pumped by means of pulsed laser energy.
During the past decade, there has been a great deal of research activity directed towards the development of laser systems employing phase conjugate reflectors. The concept of phase conjugation involves the use of optionally nonlinear media, which may be activated by means of incident laser energy to restore severely distorted optical beams to their original unaberrated state. A general discussion of the principles of optical phase conjugation may be found in a publication by Concetto R. Giuliano, entitled "Applications of Optical Phase Conjugation", Physics Today, April 1981.
The principles of phase conjugation have also been employed to form a laser resonator. Such a device is disclosed in U.S. Pat. No. 4,233,571 entitled "Laser Having a Nonlinear Phase Conjugating Reflector". The laser disclosed herein is one in which one of the conventional end mirrors of the laser resonator has been replaced by a phase conjugate reflector. A variety of phase conjugate reflectors may be employed, which utilize four-wave mixing, three-wave mixing, simulated Raman scattering, stimulated Brillouin scattering, or photon echo processes. These phase conjugation principles are generally well known in the art and some are described in the Giuliano publication cited above.
Current research has been directed towards the use of phase conjugate reflectors in optical resonators to produce a new class of lasers whose output is characterized by beams of high spatial quality. However, for these lasers to properly exhibit their intrinsic advantages, it is imperative that the phase conjugate reflectors, as well as intracavity amplifiers, maintain moderately high values of reflection and amplification, respectively, over time durations that are at least an order of magnitude larger than the resonator cavity round-trip time. This constraint often imposes severe optical energy requirements on the lasers used to pump the phase conjugate reflectors and amplifiers. The high peak powers needed over long time durations often result in thermal problems, making CW operation with high speed phase-conjugate reflectors very difficult.
Thus, it would be an improvement in the laser art to provide a laser system in which the pumping requirements of both phase conjugate reflectors and intracavity amplifiers is minimized. It would also be an advantage to have a laser system which allows for both improved phase conjugation efficiencies and amplifier gain, while requiring only modest average power requirements. It would also be an improvement to provide a laser system in which the thermal problems and overall energy demands placed on the pump lasers are reduced. It would be a further improvement to provide a phase conjugate laser system which is designed for short pulse output.